Rough idle, hard start... Bad gas?

I brought home my xs400 in April, put fresh gas with stabilizer in it and started her up for the first time in 30ish years. Bike seemed to run great but I didn't have much time to mess with it. Since then I've started the bike 1 or 2 times a week and let it run for 10 minutes or so. I recently left town for 2 weeks. When I came home the bike wouldn't start. I eventually got it started but it runs rough now. She coughs and pops and won't idle long on her own without dieing. Am I right to assume that the fuel in the tank might be old enough to be causing these issues? How long does gas last in the tank before becoming crap? Is there something else I should be looking at besides fuel?

Thanks!

CLEAN THE CARBS.................... ok and yes the fuel is probably crap.......I try to use only non ethanol fuel in all my stuff if it sits.

I have to say the first thing to do to these old bikes is pull the carbs and clean them.......then clean them again......you cant clean these things enough if you ask me......anything can make them run like crap and well todays fuel doesnt help at all..............

Best bet is to clean the carbs. Even if you only clean the jets which is the easiest thing to do on the cards. Then empty the gas tank and have a look. If the bike has been sitting there will no doubt be rust in the tank. Also consider a fuel filter. If you put stabilized gas in the bike in April fuel degradation should not be a problem. Also check the fuel lines for decay.

Personally, I wont let gas sit for more than 3 weeks... A month max. I usually keep a 1 gallon gas can for the 2 stroke, projects, or just in case. If I dont use it within that time, I dump it in my car. The stabilizer helps.

I store my bike dry of fuel and put the empty gas tank in the attic. The tank, engine intake/cylinders, and inside of the carbs get sprayed with a fogging oil and then I wrap the carbs up and put them in a box.

Batteries also suffer from long term storage. Not sure if the older style batteries that you need to fill yourself count though if thats what you have.